Specific interaction of aqueous solutions of cyclodextrin derivatives has been investigated with respect to the isomers hexane and 2,3-dimethylbutane.Saturated vapour of hexane or 2,3-dimethylbutane is equilibrated with aqueous solutions of different concentrations of cyclodextrin derivatives at 1, 10, 20, 30 and 40". The solubilities of the hydrocarbons in these solutions and in water are measured gaschromatographically. It appears that linear interaction isotherms are formed, from which the degree of occupation of the cyclodextrin voids can be calculated, assuming for the present a 1 : 1 composition of the inclusion complex.The complex association constant has been calculated for the equilibrium : saturated vapour $-cyclodextrin derivative kq inclusion complex.Plots of the natural logarithms of the association constants vs I/T show linear relationships. The standard molar values of the free enthalpy, enthalpy and entropy pertaining to the above-mentioned equilibrium have been calculated.
Inclusion compounds with cyclodextrins in aqueous solution are only known in case the included compound is a polar substance; with apolar substances only very slightly soluble inclusion compounds are formed.
In order to be able to make inclusion compounds with apolar substances in solution, hydrophylic cyclodextrin derivatives have been prepared, viz. the carboxymethylether Na‐salt, the sulfopropylether Na‐salt and a soluble epichlorohydrin resin of both a and ß cyclodextrin. The molecular weight (apparent void concentration, respectively) of the derivatives is determined in a number of different ways.
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